On my old Sino SD2 it appears that the display may be dimmed when in any mode that doesn’t read the scales. Can’t be sure this applies to everything but it’s certainly true for all the functions I’ve used.
According to Mrs Google the key presses needed to get into start up and function setting modes vary depending on which model Sino you have. So you need to find a manual.
If its not running through its self test and start up routine properly you may have an iffy membrane switch somewhere that is still making some sort of contact. Mine doesn’t actually show anything on start up, its good 30 seconds while its counting its chips and doing its bleary eyed in the morning thing before teh display wakes up.
Clive